Lung function reference values in Iranian adolescents.

There is insufficient information about reference values for pulmonary volumes for Iranian populations. A study of lung function parameters was made on 302 non-smoking healthy Iranian students (152 male and 150 female). Lung function measures correlated strongly with height but not with body mass index. There were significant differences between some of the measured parameters and American Thoracic Society reference values for Caucasians (P < 0.05). Of note is the high functional residual capacity (110% higher) and low inspirational capacity (86% lower) in males compared with the reference values.

Lung function reference values in Iranian adolescents

There is insufficient information about reference values for pulmonary volumes for Iranian populations. A study of lung function parameters was made on 302 non-smoking healthy Iranian students [152 male and 150 female]. Lung function measures correlated strongly with height but not with body mass index. There were significant differences between some of the measured parameters and American Thoracic Society reference values for Caucasians [P < 0.05]. Of note is the high functional residual capacity [110% higher] and low inspirational capacity [86% lower] in males compared with the reference values

Neighboring group catalysis in the design of nucleotide prodrugs.

An approach is described for potential application to the delivery of polar nucleosides and nucleotides across lipophilic membranes, namely, nucleotide prodrugs based on salicyl phosphate. 3'-Azido-3'-deoxythymidine (AZT) and 3'-deoxythymidine (ddT) were chosen as models. For the synthesis of prototype compounds 1 and 2, the approach was first to react either methyl salicylate (for 1) or phenyl salicylate (for 2) with phosphorus oxychloride in dry methylene chloride at 0 degree C with the addition of triethylamine as acid scavenger. The resulting intermediate phosphorodichloridate was reacted immediately with excess nucleoside under the same conditions. The control model compound 3 was prepared by reaction of phenyl phosphorodichloridate and excess nucleoside in pyridine/methylene chloride at 0 degree C to give 3 in 82% yield. The synthesis of triester 7 involved reaction of alpha-(chloroacetyl)salicyl chloride with 2,3,4,6-tetra-O-benzyl-D-glucopyranose to give [[(2,3,4,6-tetra-O-benzyl-D-glucopyranosyl)-oxy]carbonyl]-2- (1-chloroacetoxy)benzene (4) which was dechloroacetylated to 5,2,3,4,6-tetra-O-benzyl-D-glucopyranosyl salicylate. Phosphorylation of 5 with phosphorus oxychloride provided the phosphorodichloridate which was directly converted to 6 by reaction with dideoxythymidine. Removal of benzyl groups by catalytic hydrogenation gave compound 7, bis(2',3'-dideoxythymidin-5'-yl) D-glucopyranosyl phosphate. The AZT prodrug triesters, 1 and 2, underwent much more rapid hydrolysis than the triester 3, most probably due to the formation of an acyl phosphate complex from the attack on phosphorus of the salicylate carboxylate. The hydrolysis of the less lipophilic 7 was significantly slower than that of 1 or 2. Both pig liver esterase and rat brain cytosol were able to effect the cleavage to dinucleotide or mononucleotide of prodrug forms 2 and 7, much more rapidly than either 3 or 1, suggesting that the esterase-like enzymatic activity of rat brain was similar to that of pig liver esterase. This study suggests the possibility of use of salicylic acid-based prodrugs for nucleotides, subject to specific refinements in the choice of carboxylate- and phosphoric acid ester-protecting groups.

Synthesis and biological activities of a phosphorodithioate analog of 2',5'-oligoadenylate.

To enhance the resistance of 2-5A (pppA2'p5'A2'p5'A) to degradation by exo- and endonucleases, a phosphorodithioate analog was synthesized using a solid-phase phosphite triester approach with N6-benzoyl-5'-O-dimethoxytrityl-3'-O-t-butyldimethylsilyladenosine 2'-[S-(beta-thiobenzoylethyl)-pyrrolidinophosphorothioamidit e]. 5'-Monophosphorylation was accomplished with 2-[2-(4,4'-dimethoxytrityloxy)-ethylsulfonyl]ethyl-(2-cyanoe thyl)-(N,N- diisopropyl)-phosphoramidite. The resulting product, p5'A2'(s2p)- 5'A2'(s2p)5'A, was approximately 10-fold less effective as an activator of purified human recombinant 2-5A-dependent RNase than was 2-5A itself. This loss of activation ability was related directly to the loss of binding ability of the phosphorodiothioate analog. As predicted, p5'A2'(s2p)5'A2' (s2p)5'A was stable to snake venom phosphodiesterase and the nucleolytic activities of both human lymphoblastoid CEM cell extracts and human serum, under conditions that led to facile degradation of parent 2-5A. This nuclease stability permitted the observation of the CEM cell extracts and human serum phosphatase activity which led to 5'-dephosphorylation of p5'A2'(s2p)5'A2'(s2p)5'A.

2',5'-Oligoadenylate:antisense chimeras--synthesis and properties.

We have synthesized a novel bioconjugate which joins an antisense oligonucleotide to a unique and potent inhibitor of translation,pn5'A2'(p5'A2')mp5'A(2-5A). Two residues of 4-hydroxybutyl phosphate were employed as linkers to attach the 2',5'-oligoadenylate moiety through its 2'-terminus to the 5'-terminus of the chosen antisense sequence, (dT)20. The syntheses were carried on a solid support according to the phosphite triester method of DNA synthesis (Letsinger, R.L., Lunsford, W.B. (1976) J. Am. Chem. Soc. 98, 3655-3661; Beaucage, S.L., and Caruthers, M.H. (1981) Tetrahedron Lett. 22, 1859-1862). The generated 2-5A antisense chimeras retained both the ability of the 2-5A molecule to activate the 2-5A-dependent RNase as well as the ability of the oligo(dT) moiety to hybridize to the complementary poly(A). Moreover, the chimera, when annealed to its target nucleic acid sequence, was still effectively bound to the 2-5A-dependent nuclease. The methodology described represents a new approach to the selective modulation of mRNA expression.

A mathematical model of the human ventilatory response to isocapnic hypoxia.

A mathematical model of the ventilatory response to a period of sustained isocapnic hypoxia in humans has been developed. After a step into hypoxia, there is an initial rapid increase in ventilation (on-transient) followed by a slow decline. At the relief of hypoxia, there is a rapid decrease in ventilation (off-transient); the magnitude of this off-transient is smaller than that of the on-transient. Previously, the asymmetry between the on- and off-transients has been dealt with by modeling the steps into and out of hypoxia separately. The current objective was to model the whole of the response by allowing the peripheral sensitivity to hypoxia to decline during the sustained exposure to hypoxia. The model was fitted to breath-by-breath data from 20-min periods of hypoxia (end-tidal oxygen 50 Torr) at two different levels of end-tidal carbon dioxide tension from five subjects. The model was able to describe the features of the ventilatory changes well, including the slow decline and the asymmetry.

Synthesis and pharmacokinetics of a dihydropyridine chemical delivery system for the antiimmunodeficiency virus agent dideoxycytidine.

In order to explore the possibility that a dihydropyridine/pyridinium redox chemical delivery system might enhance significantly the brain uptake of the anti-HIV agent dideoxycytidine (DDC), we prepared a DDC derivative which bore the 1,4-dihydro-1-methyl-3-pyridylcarbonyl moiety at both the cytidine exocyclic amino moiety and the sugar 5'-hydroxyl function; namely, 5',4N-bis-[(1,4-dihydro-1-methyl-3-pyridinyl)carbonyl]-2',3'- dideoxycytidine (2). In cell-free extracts of rat brain tissue, compound 2 was readily converted to free DDC by stepwise oxidation and hydrolysis of the dihydropyridyl groups. Time-dependent plasma and brain concentrations of DDC and 2 were determined following iv administration of 2 (49.3 mg/kg) to rats. Compound 2 could be detected in brain, reaching peak concentrations of 7.7 +/- 2.9 nmol/g at 15 min. Low levels of DDC also were detected with a peak concentration of 1.4 +/- 0.5 nmol/g at 240 min after injection. The brain/plasma concentration integral of compound 2 was 0.95 whereas that for DDC in brain as a ratio of combined DDC and compound 2 levels in plasma was 0.24. Despite this, brain concentrations remained low and not significantly different from those achieved following administration of DDC alone.

Targeting RNA for degradation with a (2'-5')oligoadenylate-antisense chimera.

Antisense oligonucleotides hold considerable promise both as research tools for inhibiting gene expression and as agents for the treatment of a myriad of human diseases. However, targeted destruction of RNA has been difficult to achieve in a versatile, efficient, and reliable manner. We have developed an effective strategy for cleaving unique RNA sequences with 2-5A-dependent RNase, an endoribonuclease that mediates inhibitory effects of interferon on virus infection and is activated by 5'-phosphorylated 2'-5'-linked oligoadenylates known as 2-5A [pn5' A2'(p5' A2')mp5'A], resulting in the cleavage of single-stranded RNA predominantly after UpUp and UpAp sequences. To direct 2-5A-dependent RNase to cleave unique RNA sequences, p5' A2' p5' A2'p5'A was covalently linked to an antisense oligonucleotide to yield a chimeric molecule (2-5A:AS). The antisense oligonucleotide component of 2-5A:AS bound a specific RNA sequence while the accompanying 2-5A component activated 2-5A-dependent RNase, thereby causing the cleavage of the RNA in the targeted sequence. This strategy was demonstrated by inducing specific cleavage within a modified human immunodeficiency virus type 1 vif mRNA in a cell-free system from human lymphoblastoid cells. Because 2-5A-dependent RNase is present in most mammalian cells, the control of gene expression based on this technology--including therapies for cancer, viral infections, and certain genetic diseases--can be envisioned.

Hypoxic depression of ventilation in humans: alternative models for the chemoreflexes.

The ventilatory responses of 5 volunteers to three protocols were determined. In protocol A, PETCO2 was held at 1-2 Torr above resting; and PETO2 at 100 Torr for 10 min, 50 Torr for 20 min, and 100 Torr again for 10 min. In protocol B, PETCO2 was held at 8 Torr above resting, and PETO2 varied as in protocol A. Protocol C formed a control. Each protocol was repeated at least 6 times on each subject. The data were used to evaluate four different models (models 2-5) for incorporating the depressant effect of hypoxia into a standard model (model 1) of the chemoreflex responses. In model 2, hypoxic depression was incorporated as an additive term independent of the central and peripheral chemoreflexes; in model 3 it affected the central chemoreflex gain; in model 4 it affected the peripheral chemoreflex gain; and in model 5 it affected the gain of both reflexes. From this, it was concluded only model 4 was consistent with the data; all other models were inconsistent.

A comparison of indirect methods for continuous estimation of arterial PCO2 in men.

Four different measures (PETCO2, PACO2, PADCO2, and PJCO2) for indirectly estimating arterial PCO2 (PaCO2) from respired gas at the mouth have been investigated. PETCO2 was the end-tidal PCO2. PACO2 was calculated using a reconstruction of the alveolar oscillation of PCO2 obtained from the end-tidal "plateau" in PCO2. PADCO2 was calculated as for PACO2 except that the effects of dead space were incorporated. PJCO2 was calculated from an empirical relationship involving PETCO2 and tidal volume. Six subjects were studied at rest and during cycle ergometry at 50 and 100 W while breathing a variety of gas mixtures. Arterial samples were drawn for determination of true PaCO2. The differences for each method between estimated and true PaCO2 at rest and at 50 and 100 W were as follows: PETCO2, -1.35 +/- 2.64, 1.67 +/- 2.31, and 2.67 +/- 2.02 (SD) Torr; PaCO2, -2.15 +/- 2.73, -0.80 +/- 2.18, and -0.35 +/- 2.31 (SD) Torr; PADCO2, -1.55 +/- 2.54, 0.25 +/- 2.16, and 0.63 +/- 2.26 (SD) Torr; and PJCO2, -1.41 +/- 2.30, 0.12 +/- 1.79, and 0.08 +/- 1.96 (SD) Torr. It is concluded that, at rest, all methods significantly underestimate true PaCO2 and during exercise PETCO2 significantly overestimates PaCO2, but no bias was detected for any of the other methods.